The present invention relates generally to video screen display drivers, and more particularly, to a vertical sync pulse detector therefor which functions to prevent false detection of vertical sync pulses due to the presence of a copy guard signal in a video signal being displayed on the video screen display by the video screen display driver.
In general, video screen display drivers include a vertical sync pulse detector which detects vertical sync pulses included in a video signal (e.g., an NTSC composite video signal). The detected vertical sync pulses are then extracted and separated from the video signal and utilized to properly synchronize the operation of the video screen display driver (e.g., the vertical sweep circuit thereof). If this synchronization is not accurate, the on-screen video display will be distorted.
In order to prevent the unauthorized copying of video signals (e.g., video stored on a videotape) by means of a videotape recorder (VTR) , a copy guard signal is included in the video signal supplied to the VTR. The copy guard signal is generally inserted in 21 horizontal sync intervals of the video signal.
A problem which has arisen as a result of the utilization of such copy guard signals is that the vertical sync pulse detector circuit misinterprets the copy guard signal as a vertical sync pulse, thereby upsetting the synchronization of the video screen display driver, and consequently, distorting the on-screen video display.
Based on the above, it can be appreciated that there presently exists a need for a video sync pulse detector circuit which eliminates the above-identified problem with presently available video sync pulse detector circuits. The present invention fulfills this need.